Add config and service subcommands

config subcommand — show, path, edit ($EDITOR), and a non-interactive
set that takes --prefix / --compat-dir / --gameid. Lets users retarget
the Wine prefix without hand-editing TOML.

service subcommand — install / uninstall / status for a systemd --user
unit that autostarts the tray. install writes ~/.config/systemd/user/
battlenet-manager.service with ExecStart pointing at the current binary,
then daemon-reloads and enable --now's the unit. uninstall tears it back
down.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/service.rs

@@ -0,0 +1,98 @@
+use anyhow::{bail, Context, Result};
+use std::path::PathBuf;
+use std::process::Command;
+
+const UNIT_NAME: &str = "battlenet-manager.service";
+
+fn unit_path() -> Result<PathBuf> {
+    let home = std::env::var("HOME").context("$HOME is not set")?;
+    Ok(PathBuf::from(home)
+        .join(".config/systemd/user")
+        .join(UNIT_NAME))
+}
+
+fn render_unit(exe: &std::path::Path) -> String {
+    format!(
+        "[Unit]\n\
+         Description=Battle.net tray manager\n\
+         After=graphical-session.target\n\
+         PartOf=graphical-session.target\n\
+         \n\
+         [Service]\n\
+         ExecStart={exe}\n\
+         Restart=on-failure\n\
+         RestartSec=5\n\
+         \n\
+         [Install]\n\
+         WantedBy=graphical-session.target\n",
+        exe = exe.display(),
+    )
+}
+
+fn systemctl(args: &[&str]) -> Result<()> {
+    let status = Command::new("systemctl")
+        .arg("--user")
+        .args(args)
+        .status()
+        .context("Failed to invoke systemctl --user (is systemd installed?)")?;
+    if !status.success() {
+        bail!("systemctl --user {} exited non-zero", args.join(" "));
+    }
+    Ok(())
+}
+
+/// Write the unit, reload systemd, and enable+start the service.
+pub fn install() -> Result<()> {
+    let exe = std::env::current_exe()
+        .context("Cannot determine path to own executable")?;
+    let path = unit_path()?;
+
+    if let Some(parent) = path.parent() {
+        std::fs::create_dir_all(parent)
+            .with_context(|| format!("Failed to create {parent:?}"))?;
+    }
+
+    let contents = render_unit(&exe);
+    std::fs::write(&path, &contents)
+        .with_context(|| format!("Failed to write unit file {path:?}"))?;
+    println!("Wrote unit: {}", path.display());
+    println!("ExecStart: {}", exe.display());
+    println!();
+
+    systemctl(&["daemon-reload"])?;
+    systemctl(&["enable", "--now", UNIT_NAME])?;
+
+    println!();
+    println!("\x1b[1;32m✓\x1b[0m Service installed and started.");
+    println!("  Status:  systemctl --user status {UNIT_NAME}");
+    println!("  Logs:    journalctl --user -u {UNIT_NAME} -f");
+    Ok(())
+}
+
+/// Stop, disable, and remove the unit file.
+pub fn uninstall() -> Result<()> {
+    let path = unit_path()?;
+
+    // Ignore failures: the unit may already be stopped or unknown to systemd.
+    let _ = systemctl(&["disable", "--now", UNIT_NAME]);
+
+    if path.exists() {
+        std::fs::remove_file(&path)
+            .with_context(|| format!("Failed to remove {path:?}"))?;
+        println!("Removed {}", path.display());
+    } else {
+        println!("No unit file at {}", path.display());
+    }
+
+    let _ = systemctl(&["daemon-reload"]);
+    println!("\x1b[1;32m✓\x1b[0m Service removed.");
+    Ok(())
+}
+
+/// Pass through `systemctl --user status`.
+pub fn status() -> Result<()> {
+    let _ = Command::new("systemctl")
+        .args(["--user", "status", UNIT_NAME])
+        .status();
+    Ok(())
+}